JPH03249125A - Production of permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a permanent magnet having superior magnetic properties by subjecting an alloy having a specific composition consisting of rare earth elements, transition metals, B, and Ag to heat treatment under specific conditions. CONSTITUTION:An alloy having a composition consisting of, by atom, 8-30% rare earth elements including Y, particularly, Pr, Nd, etc., 2-28% B, <=6% Ag, and the balance transition metals, such as Fe, is refined and cast. The resulting cast alloy is heated at >=800 deg.C, e.g. for 24hr and then cooled rapidly through the temp. range down to 200 deg.C at >=1 deg.C/sec cooling rate. By this method, the rare earth-transition metal-B-Ag permanent magnet excellent in magnetic properties, such as residual magnetic flux density, coercive force, and maximum energy product, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a permanent magnet whose main components are rare earth elements, transition metals, boron, and silver.

[Prior Art] Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers.

With the recent demand for smaller and more efficient electrical products, permanent magnets are also required to have increasingly higher performance.

Representative permanent magnets currently in use are alnico hard ferrite and rare earth-transition metal magnets. In particular, R-Co permanent magnets and R-Fe-B permanent magnets, which are rare earth-transition metal magnets, have been extensively researched and developed because they provide high magnetic performance.

Conventionally, there are methods for manufacturing these R-Fe-B permanent magnets as shown in the following literature.

(1) A sintering method based on powder metallurgy (References 1 and 2) (2) A quenched thin piece with a thickness of about 30 μm is made using a quenched thin body production device used to produce an amorphous alloy. A resin bonding method using quenched flakes made by melt spinning to make magnets using a resin bonding method.

(References 3 and 4) (3) A method of mechanically orienting the rapidly cooled flakes used in the method (2) above using a two-step hot press;
(Document 4, Document 5) Here, Document 1; JP-A-59-46008 Document 2; M,
Sagawa, S., Fujiwara, N., Tog.
awa, H, Yamamoto and Y, Mat
uura; J, Appl, Phys, Vol.
, 55(6)15 March 1984 p2083
Reference 4; R, W, Lee; Appl, Phys;
Lett, Vol, 46(8)15 April 1
985 p790 Document 5; Japanese Patent Application Laid-open No. 100402/1985 Next, the above conventional method will be explained in detail.

In the sintering method (1), an alloy ingot is created by melting and casting, and is crushed to obtain magnets with an appropriate particle size (several μm). Magnet powder is kneaded with a binder as a molding aid,
A compact is completed by press forming in a magnetic field. This compact is sintered in argon at a temperature of around 1100° C. for about 1 hour, and then rapidly cooled to room temperature. Thereafter, the coercive force is improved by heat treatment at a temperature of around 600°C.

In the resin bonding method (2) using quenched flakes by the melt spinning method, first, a quenched ribbon of R-T M-B alloy is made at an optimal rotation speed of a quenched ribbon manufacturing apparatus. The obtained ribbon with a thickness of about 30 μm is a collection of crystals with a diameter of 1000 angstroms or less, is brittle and easily breaks, and the crystal grains are distributed in the same direction. For this reason, crystallization does not provide anisotropy and is isotropic.

A bonded magnet can be changed by crushing this flake to an appropriate size, mixing it with resin, and press-molding it. At this time 7t
Filling of about 85% by volume is possible at a pressure of about /am2.

In method (3), the quenched ribbon or piece of ribbon obtained in (2) is heated in a vacuum or in an inert atmosphere for approximately 700 minutes.
Place in graphite or other heat-resistant press mold preheated at °C. Uniaxial pressure is applied when the flake reaches the desired temperature.

Although the temperature and pressure are not specified, 725±25° C. and about 1.4 t/cm 2 are suitable as conditions for obtaining sufficient plasticity. At this stage, although the axis of easy magnetization of the magnet is slightly oriented in the pressing direction, it is generally equidirectional. The second hot press is performed in a mold with a large area. Generally, it is pressed at 700°C and 0.7 t/cm2 for several seconds. Then, the magnet becomes approximately 1/2 of its original size, the axis of easy magnetization is oriented parallel to the pressing direction, and the magnet becomes anisotropic. An R-TMB permanent magnet having anisotropy can be obtained by this direction force.

Note that the crystal grains of the rapidly quenched thin body produced by the initial melt spinning method are made smaller than the grain size at which it exhibits its maximum coercive force, so that coarsening of the crystal grains may occur during subsequent hot pressing. to obtain the optimum particle size.

However, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force, making it impossible to produce a practical permanent magnet.

[Problem M to be Solved by the Invention] Although it is possible to manufacture R-TM-B permanent magnets by using the above-mentioned conventional techniques, these manufacturing methods have the following drawbacks.

In the sintering method (1), it is essential to turn the alloy into powder, but R-T M-B permanent magnets are very active against oxygen, so it is necessary to go through the process of turning the alloy into powder. The surface area increases, oxidation becomes more intense, and the oxygen temperature in the sintered body inevitably rises. Also, when compacting the powder, a compacting aid, such as zinc stearate, must be used; although this is removed beforehand during the sintering process, the dispersion remains in the form of carbon in the magnet. This remaining carbon is undesirable because it deteriorates the magnetic performance of the R-T M-B permanent magnet.

The molded body after press molding with the addition of a molding aid is called a green body. This is very fragile and difficult to handle. Therefore, another major drawback is that it takes a considerable amount of effort to arrange them neatly in a sintering furnace.

Furthermore, in order to obtain an anisotropic magnet, press molding must be performed in a magnetic field, which requires large equipment such as a magnetic field power source and a coil.

Because of the above drawbacks, generally speaking, manufacturing R-TM-B sintered magnets not only requires expensive equipment, but also reduces production efficiency and increases magnet manufacturing costs. Therefore, R-TM-B, which uses relatively cheap raw materials,
It is difficult to say that the advantages of magnets can be fully utilized.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very low productivity and is expensive.

Since the method (2) is isotropic in principle, the energy product is low, and the squareness of the hysteresis loop is not good, so it is disadvantageous in terms of temperature characteristics and usage.

Although method (3) yields an anisotropic magnet, since hot pressing is used in two stages, it cannot be denied that it will be extremely inefficient when considering mass production.

Further, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force, making it impossible to produce a practical permanent magnet.

The present invention solves the above-mentioned drawbacks of the prior art,
The aim is to create a permanent R-TM-B-Ag system with high performance and low cost by using rare earths, transition metals, boron, and silver as basic components, and using a melting and casting process as the basis, followed by rapid cooling after heat treatment. The purpose of the present invention is to provide a method for manufacturing a magnet.

[Means for Solving the Problems] The first method of manufacturing a permanent magnet of the present invention is a method of manufacturing a permanent magnet whose basic components are a rare earth element (including yttrium), a transition metal, boron, and silver. At least a step of melting and casting an alloy consisting of the basic components;
This is a manufacturing process for permanent magnets characterized by a step of heat treatment at a temperature of 800°C or higher after casting and then rapid cooling. A method for manufacturing a permanent magnet having basic components includes at least a step of melting and casting an alloy consisting of the basic components, a step of heat treatment after casting at a temperature of 300° C. or higher, and then quenching, followed by a step of heat treatment at a temperature of 300° C. or higher and then quenching. A method for manufacturing a permanent magnet, characterized by comprising the steps of:

[Function] As mentioned above, the sintering method and the quenching method, which are conventional methods for manufacturing R-T M-B permanent magnets, each have major drawbacks such as difficulty in powder control through pulverization and poor productivity. There is.

In order to improve these drawbacks, the present inventors focused on research on magnetic hardening in the bulk state, and conducted post-casting heat treatment in the composition range of magnets whose basic components are rare earth elements, transition metals, and boron. It was discovered that the coercive force can be sufficiently high just by applying it. This method will be explained below.

The magnet using the manufacturing method of the present invention is also different from the conventional technology (
Like the magnet using the sintering method in 1), its initial magnetization curve shows a steep rise like SmCo5, which indicates that the coercive force mechanism itself is of the nucleation type. Coercive force of this type of magnet #!
The transverse direction is basically explained by the single domain model, and the coercive force of a magnet is largely dependent on its grain size. In other words, if the crystal grains of the R 2 T M + a B compound phase, which is the main phase of the R-TM-B permanent magnet and has large magnetocrystalline anisotropy, are too large, the crystal grains may have domain walls. The magnetization reversal occurs easily due to the movement of the domain wall, and the coercive force becomes smaller. On the other hand, when the grain size is below a certain critical radius, the grain becomes a single-domain grain without a domain wall.
Reversal of magnetization proceeds only by rotation. This reversal of magnetization requires greater energy than movement of domain walls, so a large coercive force can be obtained. In other words, in order to obtain a sufficiently large coercive force, the main phase R
It is necessary to set the crystal grains of the 2 T M + a B compound phase to an appropriate size.

Although this critical radius is on the order of submicrons, the grain size in the sintering method is about 10 μm. In the case of the sintering method, the cast ingot is once crushed.
If you try to obtain powder with a particle size close to the critical radius, the surface area will increase significantly and the oxygen concentration remaining in the sintered body will increase. This means that it cannot be created. On the contrary, nucleat
If it is an ion type magnet, the growth of coarse columnar or equiaxed crystals can be suppressed by adjusting the cooling rate without going through the process of pulverizing the cast ingot, and the R2
If the crystal grains of the T M + a B compound phase can be made finer, a sufficiently high coercive force can be obtained.

In the present invention, the following facts were discovered by using a composition in which silver was added to the conventional R-TM-B alloy as a basic component and optimizing the heat treatment after casting.

Ag has a lower eutectic temperature in the R-Ag binary system than in the R-Fe binary system, which explains the actual effect of Ag addition. A
By gm addition, the energy product and coercive force are increased both as a cast magnet in which the ingot is simply heat treated without hot working, and as an anisotropic magnet after hot working. The effect of Ag is significantly different from other elements that are effective in increasing coercive force, such as Dy. That is, DV increases the anisotropic magnetic field of the main phase by replacing the rare earth element in the main phase of the main magnet as R2-XD yXFe+aB, and as a result, the coercive force increases. However, in the case of Ag, rather than replacing Fe in the main phase, it mainly exists together with rare earths in the rare earth-rich phase at grain boundaries.

As is well known, the coercive force of an R-Fe-B magnet is hardly obtained only by the R2Fe+4B phase as the main phase, but is only obtained by the coexistence of a rare earth rich phase which is a grain boundary phase. Ag is considered to be an element that affects the grain boundary phase.

In alloys containing silver in this way, good magnetic performance was obtained by heat-treating the cast ingots at high temperatures and then rapidly cooling them.

Due to the above points, there is no need to go through the processes such as pulverization and sintering as described above, and productivity problems such as difficulty in powder management are eliminated.

The preferred composition range of the permanent magnet according to the present invention will be explained below.

Rare earth metals include Y, La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, and Lu are listed as candidates, and one type or a combination of two or more of these can be used. The highest magnetic performance is Pr, N
Obtained by d. Therefore, practically Pr, Nd,
Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used. Also, a small amount of additive elements, such as heavy rare earth element Dy,
'rb etc. are effective in improving coercive force.

The main phase of the R-Fe-B magnet is R2Fe+4B.

Therefore, if R is less than 8 at%, high magnetic performance cannot be obtained because the above compound is no longer formed and it has the same cubic structure as α-iron.On the other hand, if R exceeds 3C4 atom%, it is non-magnetic and R-rich. As the number of phases increases, the magnetic properties deteriorate significantly. Therefore, the appropriate range of R is 8 to 30 atomic %.

B is an essential element for forming the R2Fe+4B phase, and if it is less than 2 atomic %, it becomes a rhombohedral R-Fe system.
High coercive force cannot be expected. Moreover, when it exceeds 28 at %, the amount of B-rich nonmagnetic phase increases, and the residual magnetic flux density decreases significantly. In order to obtain a high coercive force, preferably Bj! If the coercive force is less than %, it is not possible to obtain a fine R2Fe+4B phase unless special cooling is performed, and the coercive force is small.

As mentioned above, Ag is an element that increases the energy product and coercive force by making the columnar structure finer and improving hot workability. However, since it is a non-magnetic element, if the amount added is extremely increased, the residual magnetic flux density will decrease, so it is preferably 6 at % or less.

[Example] (Example 1) A process diagram of the manufacturing method according to the present invention is shown in FIG.

The composition of the alloy used in the present invention is Pr17 atomic%
, Fe76.5W%, B5 atomic%, Ag1.5 atomic%
It is. This alloy was melted in a high frequency induction melting furnace, and a crocodile lump was cast in a mold. At this time, rare earth, iron, and silver raw materials with a purity of 99.9% were used, and boron was ferroboron.

Sample pieces were cut from this cast ingot, annealed at 1000°C for 24 hours in an argon atmosphere, and then cooled using three different cooling methods. The cooling method is
Water cooling, hearth cooling, and in-furnace cooling were used. The cooling rate is 5X10'℃/S from 1000℃ to room temperature for water cooling.
, 1℃/S from 1000℃ to 200℃ for hearth cooling
, 10 publications covering in-furnace cooling from 1000℃ to 200℃.
It was done with C/S. The results of the magnetic performance thus obtained are shown in Table 1. According to this, the performance of the reactor coolant, which has the slowest cooling rate, is lower than the other two in terms of residual magnetization, coercive force, and maximum energy product. However, with water cooling and hearth cooling, there was not much difference in performance and good magnetic performance was obtained.

Table 1 From the above, it was found that high magnetic performance could be obtained by rapidly cooling the ingot after heat treatment.

(Example 2) After melting and casting an alloy having the same composition as the alloy shown in Example 1 in a high-frequency induction furnace, a sample piece was cut out from the ingot.
600℃, 700℃, 800℃ in argon atmosphere
Heat treatment was performed at each temperature of 900°C and 900°C for 24 hours. After that, 200" from each heat treatment temperature by hearth cooling.
The temperature range up to C was rapidly cooled at a cooling rate of about 1° C./S. The magnetic performance obtained through such a process is shown in Table 2.

Table 2 From the above, it was found that excellent magnetic performance could be obtained by rapidly cooling after heat treatment at a temperature of 800'C or higher as the -stage heat treatment.

(Example 3) After melting and casting an alloy having the same composition as the alloy shown in Example 1,
A sample piece was cut from the ingot, heat treated at 1000°C for 24 hours in an argon atmosphere, rapidly cooled by hearth cooling, and then subjected to second heat treatment at 500°C, 600°C, 70°C
Heat treatment was performed at each temperature of 0°C and 800°C for 2 hours, and then the temperature range from each heat treatment temperature to 200°C was rapidly cooled by hearth cooling at a cooling rate of about 1°C/S. As is clear from the magnetic performance results obtained through this process in Figure 2, when the second heat treatment was performed at 800°C, residual magnetization, coercive force, and maximum energy product were all good. A value was obtained.

On the other hand, when the second stage heat treatment temperature is low, both magnetic performances are reduced. From this, it was found that good magnetic performance could be obtained by performing the second heat treatment at 800° C. or higher, followed by rapid cooling.

(Example 4) A sample piece was cut from a cast ingot for an alloy with the same composition as the previous example, heat-treated at 1000°C for 24 hours in an argon atmosphere, cooled at the hearth, and then heat-treated at 800°C in an argon atmosphere as a second stage heat treatment. was applied. There are three types of cooling methods: water cooling, hearth cooling, and furnace cooling.
The relationship between the obtained magnetic performance and cooling rate was investigated. Table 3 shows the results.

Table 3 As a result, the magnetic performance of the furnace-cooled samples decreased, but good magnetic performance was obtained for the water-cooled and hearth-cooled samples. From this, it was found that even after the two-stage heat treatment, better magnetic performance could be obtained if the cooling after the heat treatment was performed at a rapid cooling rate of 1° C./S or more.

(Example 5) Ingots were produced by casting alloys having the respective compositions shown in Table 4 in a forging furnace. The ingot thus obtained was subjected to a first heat treatment at 1000"C for 24 hours and then rapidly cooled, followed by a second heat treatment at 800"C.
After heat treatment at °C for 2 hours, it was rapidly cooled at the hearth. The magnetic properties of such samples were measured. The results are shown in Table 5.

From Table 5, the samples to which silver was added had excellent magnetic performance, particularly excellent coercive force.

Table 4 Table 5 [Effects of the Invention] As described above, according to the present invention, by applying appropriate heat treatment to the silver-added alloy, the magnetic properties, which were the drawbacks of conventional casting methods, can be improved. It is possible to achieve performance equivalent to or better than sintered magnets. Therefore, the advantages of the casting method, such as shortening of the manufacturing process and the possibility of producing an anisotropic resin-bonded magnet, are further promoted.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing the manufacturing method according to the present invention. FIG. 2 is a diagram showing heat treatment temperature and magnetic performance according to the present invention. that's all

Claims (1)

[Claims] 1. In a method for manufacturing a permanent magnet whose basic components are a rare earth element (including Y), a transition metal, boron, and silver, at least the process of melting and casting an alloy consisting of the basic components and the heat treatment process after casting are performed. A method for manufacturing a permanent magnet, comprising the steps of performing a heat treatment step at a high temperature of 800° C. or higher, and then rapidly cooling the temperature range up to 200° C. at a cooling rate of 1° C./s or higher.